Signal edges in transmitted signals are often prominent points within the transmitted signal, which especially in measurement technology or in transmission technology lead from one signal state to another signal state.
A detector arrangement for detection of even relatively shallow signal edges of a color difference signal transmitted by amplitude modulation over a transmission line is known from Technical Bulletin TI 891023 of the Phillips company entitled "The TDA 4670 circuit for image signal reprocessing in television receivers." In this edge detector arrangement, a differentiating edge detector, which generates at its output a detector signal that depends on the type of signal edge detected, is connected to each of the two color difference transmission lines of a color television. This detector signal is differentiated again in a downstream pulse shaper of the arrangement, and then conveyed to a switching circuit with a set switching threshold. The switching signals of the edge detector arrangement generated in this manner control an analog switch in the transmission line, at the output side of which is placed a storage capacitor. The analog switch is interrupted for the duration of the switching signal of the edge detector arrangement, so that while the analog switch is in the interrupted state, the storage capacitor determines the level of the output-side transmission signal, and keeps the transmission signal for that period at the level most recently applied before the analog switch opened. After the analog switch closes again--i.e. after the end of the signal edge--the signal on the output-side transmission line changes, with the relatively short charging time of the storage capacitor, to the level of the signal state after the signal edge, so that the slope of the corrected signal edge depends only on the short charging time of the storage capacitor.
However, the shape and amplitude of the differentiation signals generated by the edge detector depend very much on the nature of the detected signal edge. If the signal edge being detected also has a relatively long edge duration, then the point in time at which the generated detection signal reaches the threshold level (which also represents the detection time of the detected signal edge) is temporally very imprecise, as depicted schematically in diagrams (a) to (c) of FIG. 1. FIG. 1(a) schematically depicts the signal edges 1.1, 1.2, and 1.3 of three transmitted electrical signals 2.1, 2.2, and 2.3, each of which rises, over an edge duration T.f, from a level P1.1, P1.2, and P1.3 to a level P2.1, P2.2, and P2.3, respectively. FIG. 1(b) schematically depicts the three associated bell-shaped detection signals 3.1, 3.2, and 3.3 of an edge detector (not described further). Also plotted in FIG. 1(b) is the reference level Ps at which the portion 4.3 of the detector signal 3.3 that exceeds this reference level generates, at the output of a threshold switch of an ordinary detector arrangement, a switching signal 6.3 depicted in FIG. 1(c). Since the three detection signals 3.1, 3.2, and 3.3 themselves have very different amplitudes and edge slopes, they pass through the reference level Ps of the detector arrangement at very different times t1, t2, or t3, although they begin at the same initial time t0. However, these different times define the switching edges 5.1, 5.2, and 5.3 for the detection time of the detected signal flanks. In many cases this kind of correlation between the detection time of the detected signal flanks and the nature of the edges of the detection signals is not tolerable.